As a Noun: 1. The act of making a mistake about a person or thing and thinking that they are another person or thing. English = confusion. Idiomatic English = mix up. 2. A situation where it is not clear what is happening. English = confusion. As a Verb or Adjective: 1. To mix up one or more separate things so that you think one of them is actually another one. English = confuse. Idiomatic English = mix up. 2. To be unable to think of something clearly or to understand it because it does not have any order or pattern. English = (be) confused. Idiomatic English = (be) mixed up. 3. To make it difficult for someone to know exactly what to do or what to think. English = confuse.